We wish to establish unicellular eucaryotic algae with rhodopsin-like photoreceptors as model systems for vision and to use the ease of genetic and biochemical manipulation of such systems to improve our knowledge of molecular mechanisms of vision. Since behavioral and physiological experiments suggest a rhodopsin-like receptor in the algal classes Chlorophyceae (green algae), Prasinophyceae, and Dinophyceae, we wish to determine the nature of this receptor in one algal species. A wall-less mutant of Chlamydomonas (Chlorophyceae) will be cell fractionated for its receptor membrane, taking advantage of the receptor's known location, its unique spectral absorption, its probable glycoprotein nature and its possible retinal chromophore. Electron microscopy will be used to monitor each stage of the isolation. If the receptor is a rhodopsin it should be possible to determine the photoisomerization by spectrophotometric methods. Finally, the mechanisms of sensory transduction and communication of the signal to the flagellum will be studied using 1) pharmacological methods combined with extracellular recording or fluorescent membrane potential dye measurements on Chlamydomonas, 2) white noise, step, and pulse stimuli in an unique behavioral assay system utilizing a mutant of Chlamydomonas, 3) intracellular electrical recording methods on the large zoospores of the green alga, oedogonium, and 4) characterization of the present collection of Chlamydomonas phototactic mutants. An example of the use of mutants would be to study those more susceptible to normal photodamage seeking enzymes responsible for protective maintenance of normal function. We expect to find mutants corresponding to aberrant proteins at every stage of the visual process.